Concerning stereochemical assignments from 13C spectra of systems experiencing γ substituent effects. Deshielding antiperiplanar interactions can mislead the unwary

1976 ◽  
Vol 54 (20) ◽  
pp. 3272-3275 ◽  
Author(s):  
W. A. Ayer ◽  
L. M. Browne ◽  
S. Fung ◽  
J. B. Stothers
Keyword(s):  
Substituent Effects ◽  
Methyl Groups ◽  
Hydroxyl Groups ◽  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
Cis And Trans ◽  
Quaternary Carbons

A variety of substituents bonded to quaternary carbons exert marked deshielding effects at antiperiplanar γ carbons. The shifts produced by methyl groups are ca. 2 ppm, while hydroxyl groups cause shifts as large as 6 ppm. These shifts are particularly clearly demonstrated by the C-19 shieldings in 5α-substituted steroids. For 9,10-disubstituted decalins, the effect is such that cis and trans isomers are not easily distinguished from their 13C spectra. These shifts contrast sharply with the corresponding effects found for substituents bonded to less highly substituted carbon skeletons.

Merostabilization in radical ions, triplets, and biradicals. 5. The thermal cis–trans isomerization of para-substituted tetraphenylethylenes

1981 ◽  
Vol 59 (3) ◽  
pp. 609-620 ◽  
Author(s):  
William J. Leigh ◽  
Donald R. Arnold
Keyword(s):  
Transition State ◽  
Benzene Solution ◽  
Substituent Effects ◽  
Thermal Isomerization ◽  
Radical Ions ◽  
Trans Isomers ◽  
X Ray ◽  
System A ◽  
Cis And Trans Isomers ◽  
Cis And Trans

The cis- and trans-isomers of four para-substituted (three disubstituted and one tetrasubstituted) tetraphenylethylenes have been synthesized, separated, and characterized by either dipole moment or X-ray analysis. The rates of thermal isomerization of the disubstituted derivatives in benzene solution correlate with a substituent parameter reflecting substituent effects on benzylic radical stabilities (σ•), which reflects the biradical nature of the transition state for thermal isomerization in this system. A significant rate enhancement is observed for the tetrasubstituted derivative, in which merostabilization of the transition state is possible.The Arrhenius parameters for thermal isomerization in benzene were determined. From the variation observed for the disubstituted derivatives, an estimate of 35.5 kcal mol−1 for the rotational barrier in tetraphenylethylene is obtained. The activation energy for thermal isomerization of the tetrasubstituted derivative is 2 kcal mol−1 lower than those of the other three; this provides an assessment of the importance of merostabilization in this system.The thermal isomerization of some related olefins (e.g. bianthrylidenes and indigo derivatives) is discussed in light of these results.

The first observation of cis and trans isomers for bibenzo[d]imidazole-based compounds influenced by halogen substituent effects

2014 ◽  
Vol 42 ◽  
pp. 23-28 ◽  
Author(s):  
Jiao Geng ◽  
Tao Tao ◽  
Hui-Qing Chen ◽  
Wei Huang
Keyword(s):  
Substituent Effects ◽  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
Cis And Trans

scholarly journals The Metabolism of 14C-Labeled cis and trans Isomers of Octadecenoic and Octadecadienoic Acids

1964 ◽  
Vol 239 (8) ◽  
pp. 2482-2488
Author(s):  
Katsuto Ono ◽  
Donald S. Fredrickson
Keyword(s):  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
Cis And Trans ◽  
Octadecadienoic Acids

Cis and trans isomers of 1-(5-bromothiophen-2-yl)-3-(10-chloroanthracen-9-yl)prop-2-en-1-one: Synthesis and characterization

2021 ◽  
Vol 1236 ◽  
pp. 130228
Author(s):  
P. Naresh ◽  
B. Pramodh ◽  
S. Naveen ◽  
S. Ganguly ◽  
J. Panda ◽  
...  
Keyword(s):  
Synthesis And Characterization ◽  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
Cis And Trans

scholarly journals Identification of Anthocyanin Compounds in Butterfly Pea Flowers (Clitoria ternatea L.) by Ultra Performance Liquid Chromatography/Ultraviolet Coupled to Mass Spectrometry

Molecules ◽  
2021 ◽  
Vol 26 (15) ◽  
pp. 4539
Author(s):  
Nguyen Minh Thuy ◽  
Vo Minh ◽  
Tran Ben ◽  
My Tuyen Thi Nguyen ◽  
Ho Ha ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Liquid Chromatography ◽  
Ultra Performance Liquid Chromatography ◽  
Negative Ion ◽  
Trans Isomers ◽  
Clitoria Ternatea ◽  
Flower Extract ◽  
Cis And Trans Isomers ◽  
Butterfly Pea ◽  
Cis And Trans

Butterfly pea flower have great sensory attraction, but they have not yet been used widely in Vietnam. Extracts of butterfly pea flowers can be used conveniently as a natural blue colorant for food products. In this study, the identification of anthocyanin compounds in butterfly pea flowers was performed by UPLC coupled with a UV and Mass spectrometer instrument. Positive and negative ion electrospray MS/MS chromatograms and spectra of the anthocyanin compounds were determined. By analyzing the chromatograms and spectra for each ion, five anthocyanins were identified in the butterfly pea flower extract; these were delphinidin-3-(6”‐p-coumaroyl)-rutinoside, cyanidin 3-(6”-p-coumaroyl)-rutinoside, delphinidin-3-(p-coumaroyl) glucose in both cis- and trans- isomers, cyanidin-3-(p-coumaroyl-glucoside) and delphinidin-3-pyranoside. Additionally, based on their intensity, it was determined that cyanidin-3-(p-coumaroyl-glucoside) was the most abundant anthocyanin, followed by cyanidin 3-(6”-p-coumaroyl)-rutinoside, delphinidin-3-(p-coumaroyl-glucoside), delphinidin-3-(6”-p-coumaroyl)-rutinoside and delphinidin-3-pyranoside. In this study, cyanidin derivatives were discovered in butterfly pea flower extract, where these compounds had not been detected in previous studies.

Unveiling the coexistence of cis- and trans-isomers in the hydrolysis of ZrO2: A coupled DFT and high-resolution photoelectron spectroscopy study

2020 ◽  
Vol 153 (24) ◽  
pp. 244308
Author(s):  
Ali Abou Taka ◽  
Mark C. Babin ◽  
Xianghai Sheng ◽  
Jessalyn A. DeVine ◽  
Daniel M. Neumark ◽  
...  
Keyword(s):  
High Resolution ◽  
Photoelectron Spectroscopy ◽  
Spectroscopy Study ◽  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
Cis And Trans ◽  
Hydrolysis Of

scholarly journals Separation of cis and trans Isomers of Polyproline by FAIMS Mass Spectrometry

2016 ◽  
Vol 27 (12) ◽  
pp. 2071-2074 ◽  
Author(s):  
Andrew J. Creese ◽  
Helen J. Cooper
Keyword(s):  
Mass Spectrometry ◽  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
Cis And Trans

PREPARATION OF ERUCIC AND NERVONIC ACIDS LABELLED WITH CARBON-14

1957 ◽  
Vol 35 (8) ◽  
pp. 757-760 ◽  
Author(s):  
K. K. Carroll
Keyword(s):  
Enoic Acid ◽  
Nervonic Acid ◽  
Malonic Ester ◽  
Ester Synthesis ◽  
Trans Isomers ◽  
Carbon 14 ◽  
Cis And Trans Isomers ◽  
Cis And Trans

The malonic ester synthesis of nervonic acid (tetracos-15-enoic acid) has been modified so that the product consists of pure cis rather than a mixture of cis and trans isomers. The modified synthesis has been used for the preparation of C14-labelled erucic and nervonic acids.

Synthesis of cis and trans Isomers of D-Ring Linked Bis-Steroid Pyrazines from 16α-Bromo-17-oxosteroids

2002 ◽  
Vol 67 (1) ◽  
pp. 47-54 ◽  
Author(s):  
Zenon Łotowski ◽  
Jacek W. Morzycki ◽  
Izabella S. Niewczas ◽  
Marta Zdanowicz
Keyword(s):  
Gaseous Ammonia ◽  
Analogous Reaction ◽  
Air Oxidation ◽  
Trans Isomers ◽  
Hydrolysis Products ◽  
Cis And Trans Isomers ◽  
Cis And Trans

Treatment of 16α-bromo-17-oxosteroids 1 and 2 with gaseous ammonia and successive air-oxidation afforded the cis and trans isomers of D-linked bis-steroid pyrazines. Analogous reaction of 1α-bromo-4-nor-5α-cholestan-2-one (3) led to unexpected hydrolysis products.

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